Timing circuit



Nov. 2, 1937. w LORD 2,098,052

TIMING CIRCUIT Filed March 16, 1936 Fig. I.-

A.C. SOURCE fiffimmimMAMA \JUUVVVVUUVVV m {L W KMM MAM A i nventor; Hanoi d \M' Lord.

H is Attorney, I

Patented Nov. 2, 1937 UNITED STATES PATENT OFFICE I TIMING CIRCUIT New York Application March 16, 1936, Serial No. 69,244

14 Claims.

Myinvention relates to an electric timing circuit and more particularly to electric timing circuits and to methods for providing electrical timing quantities for controlling the energization of electric valve systems.

In many electric valve circuits, and particularly in welding circuits employing electric valves, it

is desirable to control periodically the conductivity of an electric valve so that the electric valve i conductive for a predetermined interval of relatively short duration and maintained nonconductive for a predetermined succeeding interval of longer duration. Furthermore, in order to obtain precise and accurate control of the conductivity of an electric valve under these condititons, it is desirable that the voltage impressed upon the control member be of peaked wave form and have a substantially perpendicular wave front. By the use of prior art arrangements, it has been possible to meet this requirement where the ratio of the period of non-conduction to the period of conduction is not great. However, in circuits where it is essential that energy be supplied to an associated circuit for only a relatively short but accurate interval of time and where it is desirable to obtain rather long intervals of time between successive energizations, the prior art arrangements have not been found entirely satisfactory.

An object of my invention is to provide an improved electric timing circuit which obviates the above difficulty.

,Another object of my invention is to provide an improved electric timing circuit for electric valve circuits by means of which an electric valve may be rendered conductive during a predetermined interval and may be maintained non-com ductive for a predetermined succeeding interval.

A further object of my invention is to provide an improved electric timing circuit for controlling the conductivity of an electric valve by means of which the periodic voltage impressed upon the control member is of relatively short duration and has a wave shape of predetermined form.

A still further object of my invention is to provide a periodic electric timing device for electricvalve excitation circuits by means of which the electric valve may be maintained conductive for a predetermined number of half cycles of applied alternating potential and maintained nonconductive for a predetermined greater number of succeeding half cycles and by means of which the points of beginning and termination of the electrical impulses may be accurately timed,

In accordance with the illustrated embodiment of my invention, I provide an electric timing circuit' for periodically controlling the conductivity of an associated electric valve and by means of which the electric valve may be maintained conductive for a predetermined number of half cycles of applied alternating potential and maintained non-conductive for a predetermined greater number of following half cycles. I provide an electric timing device comprising a circuit of the single valve inverter type associated with an auxiliary circuit by means of which the associated electric valve to be controlled may be maintained conductive and non-conductive during predetermined intervals, and by virtue of which a relatively high ratio of the period of non-conduction to the period of conduction may be obtained. The auxiliary circuit is energized in accordance with the voltage appearing across an impedance element connected in the inverter circuit and supplies a periodic voltage of peaked wave form whereby a relatively high ratio of the period of non-conduction to the period of conduction may be obtained.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Fig. 1 diagrammatically illustrates an embodiment of my invention for controlling the conductivity of an associated electric valve, and Fig. 2 represents certain operating characteristics of the embodiment of my invention diagrammatically illustrated in Fig. 1.

Referring now to Fig. 1 of the accompanying drawing, my invention is diagrammatically shown as applied to an electric valve translating circuit in whichany suitable electronic discharge device, such as an electric valve l having an anode 2, a cathode 3 and a control member 4 is energized from an alternating current circuit 5 to supply unidirectional current to a direct current load circuit 6. In order to control the conductivity of the electric valve 6, I provide a timing circuit 1 which is energized from a source of direct current 8. A voltage divider 9 comprising resistances I0 and I! and an adjustable contact I2 is connected across the source of direct current 8. A capacitance l3 in the timing circuit 1 is employed to be periodically charged from the source of direct current 8 and discharged through an electric valve H of the vapor electric discharge type having an anode IS, a cathode l6 and a control electrode IT. The capacitance I8 is till) dill charged from the direct current source 2 through a resistance iii. A conductor it is employed to connect the positive terminal of the direct current source ii to the capacitance l3 and to an inductance 2@ which is connected in series with the electric valve it. An auxiliary circuit including a serially-connected resistance 2i and a capacitance 22 is connectedin parallel with the resistance it.

The auxiliary circuit comprising resistance 2i and capacitance 22 is energized in accordance with an electrical condition of the timing circuit including capacitance it and resistance it such as the voltage appearing across the resistance it. The value of resistance 211 is relatively large as compared with the value of resistance it, and the value of capacitance 22 is small as compared with the capacitance it.

The electric valve M is rendered conductive periodically by means of the voltage impressed between the cathode iii and the control electrode ill by the circuit comprising capacitance it! and resistance iii. The net or resultant voltage impressed upon the control electrode ll of electric valve i l comprises three components of voltage. The first and predominating component is the periodic voltage impressed between the control electrode it and the cathode it due to the periodic' energization of the circuit comprising resistance it and capacitance it. The second component of voltage impressed upon the control electrode ii is a periodic voltage supplied by a transformer 2t. The third component of voltage is the bias voltage supplied bythe voltage divider t which is impressed upon the control electrode l?! by means of a conductor 22, the secondary winding oi the transformer 24 and a resistance 2b.

The transformer 2t, preferably of the type designed to furnish a voltage of peaked wave form, is employed as a synchronizing or correlating means to control the conductivity of electric valve it at predetermined times relative tothe voltage of the alternating current source 2 which is impressed across the anode and cathode of electric valve l. The peaked voltage supplied by the transformer 2 is superimposed upon the potentials supplied by the voltage divider d and the auxiliary circuit comprising capacitance 22. Although in the embodiment of my invention illustrated in Fig. 1 l have shown a transformer 26 energized from a separate source of alternating current 263, it will be understood that the transi'ormer 2 3 may be energized from the alternating current circuit 5. The cathode it of electric valve it is connected to the resistance ill and capacitance 22 by a conductor 27!.

The auxiliary circuit comprising the resistance 2i and the capacitance 22 serves the purpose of providing a periodic electrical timing quantity which is utilized to control the'conductivity of the electric valve l. Moreover, this auxiliary cir cuit acting in conjunction with the other elements of the timing circuit 2 supplies a voltage oi peaked wave form having a substantially perpendicular wave front which is desirable in order to obtain precise and accurate control of electric valves.

Where it is desirable to obtain relatively small ratios of. period of non-conduction to period of conduction, a switch 28 having stationary contacts 2i? and hit is provided so that the control member i of electric valve 11 may be connected to terminal 3!], and where it is desirable to obtain a relatively high ratio of the period t n n-c accepts duction to the period of conduction, the switch Et'maybe employed to connect the control member d to the terminal 32 in the discharge circuit comprising resistance 26 and capacitance 22. The cathode 3 is connected to the adjustable contact 52 of voltage divider Q through conductor 33. By moving the adjustable contact l2 toward or away from the positive terminal oi resistance it, the negative bias voltage impressed on the control member t may be increased or decreased.

Although I have diagrammatically shown my invention as applied to an electric valve system in which only one electric valve is employed to transmit energy from an alternating current circuit to a direct current circuit, it will be understood by those skilled in the art that my invention in its broader aspects may be applied to electric valve translating circuits generally involving a plurality of valves and in which energy is transmitted in either direction between direct current and alternating current circuits or between alternating current circuits of the same or diflerent frequencies.

In explaining the operation of the embodiment of my invention diagrammatically illustrated in Fig. 1, it will be assumed that the capacitance i3 is not charged and that the electric valve it is maintained non-conductive by virtue of a suitable potential being impressed upon the control elec trode ill by means of the voltage divider t and through conductor v22, secondary winding of transformer 22 and resistance 25. During this period, the capacitance iii will be charged from the direct current source 2 through conductor it. conductor it and resistance it. The electric valve it is rendered conductive and efiects discharge of the capacitance I13 when the periodic control potential impressed on the control electrode ll of electric valve it through the voltage divider ll, due to the previous discharge of capacitance it, increases to a value sufficiently positive relative to the cathode ill to permit the peaked voltage of transformer 2t to render electric valve it conductive. The capacitance it will discharge through the circuit comprising the portion of conductor it between capacitance it and inductance 2t, inductance 22, electric valve M, and conductor 27!. A small portion of the energy previously stored in capacitance it is stored in the capacitance 22 and the energy stored in capacitance 22 is subsequently discharged through a circuit comprising the resistances l2 and 2t. The rate at which the voltage impressed upon the control electrode d of electric valve l increases will depend principally upon the time constant of the portion of the timing circuit comprising capacitance lit, inductance 2t and resistance it.

Referring to Diagram I of Fig. 2, the curve A represents the periodic voltage appearing between the conductor and the terminal 32 in the discharge circuit comprising resistance 25 and capacitance 22 and represents the voltage which would be impressed upon the control electrode 6 through contact Si l of switch 22. The curve B represents the periodic voltage which is impressed upon the control electrode i when the switch member 28 engages contact 29. The curve '0 represents the bias voltage which is superimposed upon the voltages appearing in the discharge circuit and the magnitude of which, relative to the periodic voltages represented by curves A and B and the control characteristic of the electric valve i, determines the interval during which the electric valve [1 is rendered conductive. The bias voltage impressed upon the control elec represented by the curve E.

Referring again to Diagram I oi Fig. 2, the interval represents the interval during which the capacitance l3 discharges through the inductance 23 and the electric valve H. The inductance 20 serves to limit the current which flows in the timing circuit 1 during the discharge P riod and also assists in the control of the electric valve l4'by impressing a transient negative potential upon the anode l3 during the latter part of the discharge period to render the valve 4 non-conductive. It will be noted that at the time rthe potential appearing between the conductor 33 and the point 32 in the discharge circuit is maximum and that this potential is sufficiently positive relative to the cathode 3 of electric valve to render the electric valve I conductive at the time 2:. Curve F of Diagram II of Fig. 2 represents the sinusoidal voltage of the alternating current circuit 5 impressed between the anode 2 and the cathode 3 of electric valve and the curve G of Diagram III represents the current which will fiow in the direct current cr cuit 6, when the control member 4 is connected to the terminal 32.

During the interval o-a: the capacitance l3 will discharge through the conductor IS, the inductance 20 and the elwtric valve l4. Since the resistance It is of relatively large value, the lower plate of the capacitance l3 will be increased in potential effecting thereby an increase in the potential of the terminal 3| relative to the conductor 33. At the time a: the electric valve I4 is rendered non-conductive by the inductance 20. Since the energization of the capacitance 22 can not be changed instantaneously. the potential of the terminal 32 will also be increased to effect an increase in potential as indicated by the portion of the curve A between the time o and the 'sistance i8 and the resistance 25.

time :0. During the interval x-z the capacitance 22 will be charged at a rate corresponding to the voltage appearing across the resistance l8. As the capacitance 22 becomes charged the voltage of the terminal 32 decreases. At the time 2. the voltage appearing across the capacitance 22 is equal to the voltage appearing across the resistance iii. It should be noted that during the interval :r-n the capacitance I3 is being charged from the direct current source 8 through the resistance i8. When the voltage appearing across the capacitance 22 equals the voltage appearing across the resistance It, the period of charging of the capacitance 22 will end, corresponding to the time 2, and the capacitance 22 will begin to discharge through a circuit comprising'the re- It should be further understood that at the time .2 the direction of current transfer through the capacitance 22 reverses, and the capacitance 22 discharges during the interval z--n.

Referring to Diagram I 01 Fig. 2, it will be noted' that during the interval :zn the voltage impressed upon the cathode iii of electric valve i4 is positive relative to the voltage impressed upon the control electrode ll, thereby maintaining electric valve l4 non-conductive. At the time n, the voltage impressed upon the cathode I6 has decreased sufiiciently to permit the voltage of peaked wave form supplied by transformer 24 and represented by curve D to render electric valve l4 conductive. This feature of periodically controlling an electric valve is disclosed and broadly claimed in my copending application 5erial No. 585,292, filed January 7, 1932, land assigned to the assignee of the present application.

Curve H of Diagram IV of Fig. 2 represents the current which will flow in the direct current circuit 3 when the control member 4 of electric valve is connected to terminal 3| by means of Q the switch 23. Since the voltage appearing across conductor 33 and terminal 3| decays at a slower rate than the voltage appearing across conductor 33 and terminal, the electric valve I will be maintained conductive for a greater number of half cycles in accordance with the characteristic illustrated by curve B of Diagram I. At the time m the voltage impressed upon the control member 4 has decreased to a value less positive than the critical control potential for the particular valve employed and the electric valve I will be maintained non-conductive until the above described operation is initiated at time 11. when the control valve i4 is again rendered ill conductive by means of the bias voltage supplied by resistances i0 and ii and the voltage of the transformer 24.

It will be noted that by virtue of my invention I provide an arrangement whereby an electric valve may be periodically rendered conductive for a relatively short interval of time and may be maintained non-conductive for a relatively long interval of time thereafter without sacrificing precision and reliability of operation.

My invention is particularly suited for con trolling the energization of electric welding circuits employing electric valves where it is desirable to obtain periodic energization of these circuits. It is frequently desirable in welding circuits to provide a periodic timing circuit to control the energization of the associated electric valves so that the electric valves supply energy to the welding circuit for a predetermined interval of time and which subsequently controls the electric valves-so that the valves are maintained non-conductive for a predetermined interval of greater duration than the period of energization. By means of my invention diagrammatically shown in Fig. 1, I may control or adjust the period or interval between succes sive energizations of an associated welding circuit by adjusting the resistance I8; and by choosing suitable values for the resistance 2| I may control the period of energization. As the value of the resistance element I8 is increased, other constants of the circuit remaining constant, the period or interval between successive energizations of the electric valve i is increased. By increasing the value of the resistance 2|, I may increase the period of energization of the electric valve i. The period of energization of electric valve I may be controlled also by adjusting the position of the adjustable contact i2. By moving the adjustable contact upward the the negative bias voltage is increased, effecting thereby a decrease in the period of conduction and an increase in the ratio of the period of nonconduction to the period of conduction of electric valve I.

While I have shown and described my invention as applied to a particular system of connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as iii fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a source of current, a circuit having a relatively large time constant comprising a capacitance arranged to be charged from said source and means for periodically discharging said capacitance, and a second circuit having a time constant small relative to that of said first-mentioned circuit and connected to he energized in accordance with an electrical condition of said first-mentioned circuit to provide a periodic timing quantity.

2. In combination, a source of current, a capacitance, a resistance through which said capacitance is charged from said source, a circuit connected in parallel with said resistance including a capacitance, and means for periodically discharging said first-mentioned capacitance to effect energization of said circuit in accordance with an electrical condition of said first-mentioned resistance to provide a periodic timing quantity.

3. In combination, a source of current, 2. capacitance, a resistance through which said capacitance is charged from said source, a circuit connected in parallel with said resistance including a capacitance, means for periodically discharging said first-mentioned capacitance, and means energized in accordance with an electrical quantity of said first-mentioned resistance for providing a periodic electrical timing quanmy having a peaked wave form.

4. In combination, a. source of current, a ca pacitance, a resistance through which said capacitance is charged from said source, means comprising an electric valve for discharging said capacitance, means for rendering said valve nonconductive, and a circuit comprising a seriallyconnected resistance and capacitance connected in parallel with said first-mentioned resistance to provide an electrical timing quantity.

5. In combination, a source of current, a circuit comprising a capacitance and a resistance connected in series and arranged to be energized from said source, a second circuit for providing an electrical timing quantity comprising a seriallyconnected resistance and capacitance connected in parallel with said first-mentioned resistance,

said second circuit having a time constant substantially less than the time constant of said firstmentioned circuit, means comprising an electric valve for periodically discharging said first-mentioned capacitance, and means for rendering said valve non-conductive.

6. In a timing device for controlling the conductivity of an electric valve means, the combination of a source of direct current, a capacitance, a resistance, a serially-connected capacitance and resistance connected in parallel with said firstmentioned resistance, and means comprising an electric valve for effecting energy transfer from said first-mentioned capacitance to said secondmentioned capacitance to provide a periodic timing quantity.

7. An electric timing device comprising a source of direct current, a voltage divider connected across said source, a capacitance, a resistance through which said capacitance is charged from said source, an auxiliary circuit comprising a serially-connected resistance md capacitance con-- nected in parallel with said first-mentioned resistan e, and means comprising a serially-connected electric valve and an inductance for periunidirectional current to said load circuit during a predetermined interval andfor effecting deenergization of said load circuit during predetermined succeeding intervals, and a timing circult for controlling the conductivity of said electric valve comprising a source of direct current, a capacitance, a resistance through which said capacitance is charged from said direct current source, an auxiliary circuit comprising a seriallyconnected resistance and capacitance connected in parallel with said first-mentioned resistance, means comprising an electric valve for discharging said first-mentioned capacitance, and means for controlling the conductivity of said secondmentioned electric valve.

9. In combination, an alternating current supply circuit, a direct current load circuit, an electric valve interconnecting said circuits, and a timing circuit for controlling said electric valve to obtain a relatively high ratio of the period of nonconduction to the period of conduction of said valves comprising a source of direct current, a capacitance, a resistance of relatively high value through which said capacitance is charged from said direct current source, a serially-connected resistance of relatively large value and a capacitance connected in parallel with said first-mentioned resistance, and means comprising an electric valve for periodically discharging said firstmentioned capacitance to efiect periodic energization of said second-mentioned capacitance in accordance with the voltage appearing across said first-mentioned resistance.

10. In combination, an alternating current supply circuit, a direct current load circuit, an electric valve having an anode, a cathode and a control member interconnecting said circuits, and a timing circuit for controlling the conductivity of said valve by impressing on said control memher a voltage of short duration and having a substantially peaked wave form comprising a source of direct current, a voltage divider connected across said source of direct current, a capacitance, a resistance of relatively small value through which said capacitance is charged from said direct current source, an auxiliary circuit comprising a serially-connected resistance of relatively large value and a capacitance connected in parallel with said first-mentioned resistance and means comprising an electric valve for periodically discharging said capacitance, and means for impressing on the control member of said firstmentioned valve a voltage which is the resultant of a negative bias voltage obtained from said voltage divider and a voltage appearing across said second mentioned resistance.

11. In combination, a source of alternating current, a load circuit, an electric valve interconnecting said circuits, and a timing circuit for controlling the energization of said electric valve comprising a source of direct current, a capaciance, a resistance, an auxiliary circuit comprising a serially-connected resistance and a capacitance connected in parallel with said first-mentioned resistance, means comprising an electric valve for discharging said first-mentioned capacitance, means for rendering said second-mentioned electric valve periodically conductive and non-conductive to provide periodic energization of said second-mentioned capacitance.

12. In combination, a source of alternating current, a load circuit, an electric valve interconnecting said circuits, and a timing circuit for controlling the conductivity of said electric valve comprising a source of direct current, a circuit including a serially-connected capacitance and resistance connected across said source, an auxiliary circuit comprising a serially-connected resistance and capacitance connected in parallel with said first-mentioned resistance, said secondmentioned circuit having a time constant substantially less than the time constant of said first-mentioned circuit, means comprising an electric valve for discharging said first-mentioned capacitance, means for controlling the conductivity of said second-mentioned valve comprising a source of periodic potential having a period greater than the period of the voltage of said alternating current circuit and means for rendering said second-mentioned valve non-conductive after said first-mentioned capacitance has discharged.

13. In combination, an alternating current circuit, a load circuit, an electric valve having an anode, a cathode and a control member interconnecting said circuits, and an electric timing circuit for controlling the conductivity of said electric valve comprising a source of direct current, a serially-connected capacitance and resistance connected across said source, an auxiliary circuit including a serially-connected resistance and capacitance connected in parallel with said first-mentioned resistance, means comprising an electric valve for discharging said first-mentioned capacitance, means for rendering said second-mentioned valve non-conductive after the period of discharge of said capacitance and means for impressing upon the control member of said first-mentioned valve a potential responsive to an electrical condition of said auxiliary circuit.

14. In combination, an alternating current supply circuit, a direct current load circuit, an electric valve having an anode, a cathode and a control member interconnecting said circuits, and a timing circuit for controlling the conductivity of said valve by impressing on said control member a voltage of predetermined period and having a peaked wave form comprising a source of direct current, a voltage divider connected in said source of direct current, a capacitance, a re sistance through which said capacitance is charged from said source, an auxiliary circuit comprising a serially-connected resistance and a capacitance connected in parallel with said firstmentioned resistance, means for periodically discharging said first-mentioned capacitance, means for impressing on the control member of said first-mentioned valve a voltage which is the resultant of a negative bias voltage obtained from said voltage divider and a voltage appearing across said second-mentioned resistance and means for adjusting said negative bias voltage to control the period of said voltage impressed upon said control member.

HAROLD W. LORD. 

